This way only for experienced users.
Small instruction. (I do not bear any responsibility)
1. load xterm
2. Change user to root "sudo gainroot"
3. apt-get install wget bzip2
4. Change directory "cd /usr/share/omweather/icons"
5. Download for example POD iconset
'wget "http://www.liquidweather.net/phpmv2/phpmyvisites.php?url=http%3A//mirror1.liquidweather.net/Pod.tar.bz2&id=1&pagename=FILE:Icons%3APod"'
6. Unpack bzip archive "bzip2 -d Pod.tar.bz2"
7. Unpack tar archive "tar xf Pod.tar"
8. Move files from Pod/large_icons directory to Pod directory "mv Pod/large_icons/* Pod"
9. Rename N/A icon "cd Pod;mv na.png 48.png"
10. Change iconset to Pod in OMWeather settings
11. This the end. Good luck

Vlad.